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1.
Among various Cu/ZnO/ZrO 2 catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO 2 obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO 2 catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO 2 catalyst with 15 wt.% of ZrO 2 turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO 2 catalysts is reduced, the Cu 2+ species present in the ZrO 2 lattice is transformed to Cu + species. This leads to the speculation that the addition of ZrO 2 to Cu/ZnO catalysts gives rise to the formation of Cu + species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO 2 catalyst in addition to Cu metal particles. Consequently, the ratio of Cu +/Cu 0 is an important factor for the specific activity of Cu/ZnO/ZrO 2 catalyst for methanol synthesis. 相似文献
2.
The H 2-TPR (temperature-programmed reduction) study was performed for supported copper oxide catalysts with low loading (0.5 wt% as copper). Among the various kinds of support materials (γ-Al 2O 3, TiO 2, ZrO 2, SiO 2, ZSM-5), alumina-supported copper oxide indicated a one-electron reduction behavior of Cu 2+ into Cu + ions in the presence of H 2. The reduction of the isolated Cu 2+ species in a tetragonally distorted octahedral symmetry into the low coordinated Cu + ions was identified by means of X-ray absorption spectroscopy (XANES and EXAFS). The isolated Cu + ions hosted by γ-Al 2O 3 surface were prevented from further reduction into metallic Cu 0 state under reducing condition with H 2 at 773 K. Less dispersed supported copper oxide species were easily reduced to Cu 0 metal particles with H 2 at 573 K regardless of the kinds of support materials. It is suggested that the one-electron redox behavior of the isolated copper oxide species over γ-Al 2O 3 promotes the catalytic reduction of NO with CO in the presence of oxygen on the basis of redox-type mechanism between Cu 2+ and Cu + in atomically dispersed state. 相似文献
3.
The effects of Zr doping on the existence of Cu and the catalytic performance of Ce 0.7−xZr xCu 0.3O 2 for CO oxidation were investigated. The characterization results showed that all samples have a cubic structure, and a small amount of Zr doping facilitates Cu 2+ ions entering the CeO 2 lattice, but excessive Zr doping leads to the formation of surface CuO crystals again. Thus, the number of oxygen vacancies caused by the Cu 2+ entering the lattice (e.g., Cu 2+–□–Ce 4+; □: oxygen vacancy), and the amount of reducible copper species caused by CuO crystals, varies with the Zr doping. Catalytic CO oxidation tests indicated that the oxygen vacancy and the reducible copper species were the adsorption and activation sites of O 2 and CO, respectively, and the cooperative effects between them accounted for the high CO oxidation activity. Thus, the samples x = 0.1 and 0.3, which possessed the most oxygen vacancy or reducible copper species, showed the best activity for CO oxidation, with full CO conversion obtained at 110 °C. The catalyst is also stable and has good resistance to water during the reaction. 相似文献
4.
The redox behavior and states of Cu ions in Cu ion-exchanged MFI (Cu( n)-MFI, n: exchange level) have been investigated by means of temperature-programmed desorption (TPD) of oxygen, diffuse reflectance (DR) UV–VIS spectroscopy and Cu + photoluminescence (PL) spectroscopy. TPD chromatograms of oxygen from Cu(n)-MFI were characterized by the appearance of three desorption peaks: (below 200°C), β (300–500°C) and γ (above 500°C). It has been suggested that and β oxygen are extra-lattice oxygen adsorbed on Cu ions, while γ oxygen is lattice oxygen coordinated to Cu ions. The Cu + emission was tremendously reduced once the catalyst contacted with O 2 and NO at elevated temperatures such as 500°C, and it was almost invisible under the working state of the catalyst, suggesting that PL-active Cu + ions are not real active sites under the working state. The desorption of β oxygen was intimately related to the creation of active centers for the NO decomposition reaction. DR measurements showed that the desorption of β oxygen caused tetragonal Cu 2+ to decrease and trigonal Cu 2+ to increase simultaneously. It has been proposed that both Cu 2+ and Cu + are involved in the NO decomposition catalysis over Cu-MFI under the working state. 相似文献
5.
The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO3/Al2O3 catalyst than on the Pd/CeO2/Al2O3 and Pd/Nb2O5/Al2O3 catalysts. The explanation for the very high N2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Meδ+ stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N2 selectivity. 相似文献
6.
The effect of ion exchange conditions, such as Si/Al ratio, precursor copper salt, pH and concentration of the solution, on the catalytic activity in SCR of NO by propane and on the electronic state of copper ions in Cu-ZSM-5 has been studied. The NO conversion in NO SCR by C 3H 8 has been found to reach a maximum value at Cu/Al ratio about 0.37–0.4 and remain constant at higher Cu/Al. ESR and UV–vis DR spectroscopy have been used to elucidate stabilization conditions of copper ions in Cu-ZSM-5 zeolites as isolated Cu2+ ions, chain copper oxide structures and square-plain oxide clusters. The ability of copper ions for reduction and reoxidation in the chain structures may be responsible for the catalytic activity of Cu-ZSM-5. These transformations of copper ions are accompanied by the observation of intervalence transitions Cu2+–Cu+ and CTLM of the chain structures in the UV–vis spectra. 相似文献
7.
A combined spectroscopic and catalytic study of the NO reactivity on microporous aluminophosphates, with chabasite-related structure, CoAPO-34, CuAPO-34 and CuAPSO-34, is reported. NO and CO adsorption were monitored by FTIR spectroscopy, and revealed that Co 2+/Co 3+ and Cu +/Cu 2+ redox couples, the sites responsible for the catalytic activity, are present in these catalysts. CoAPO-34 catalysts showed exceptionally high performances in the oxidation of NO to NO 2, and poor activity in other DeNO x reactions. Copper-based aluminophosphates and silico-aluminophosphates, besides good performances in the NO oxidation to NO 2, showed good activity in the N 2O decomposition even in the presence of oxygen or water in the feed. The presence of silicon has beneficial effects both on the thermal and hydrothermal stability of the zeolitic structure, as well as on the catalytic performances of the metal-aluminophosphates. 相似文献
8.
The perovskite-type oxides La 0.8Ce 0.2Cu 0.4Mn 0.6O 3 and La 0.8Ce 0.2Ag 0.4Mn 0.6O 3 prepared by reverse microemulsion and sol–gel methods (denoted as R and S, respectively), have been investigated on their catalytic performance for the (NO + CO) reaction, and characterized by means of temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD measurements proved the presence of the perovskite phase with a considerable amount of CeO 2 phase and the formation of CeO 2 phase was restrained with the reverse microemulsion method. TEM investigations revealed that the La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-R nanoparticles were uniform spheres in shape with diameters ranging from 40 to 50 nm, whereas an aggregation of particles was found for the La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-S catalyst. The activity of NO reduction with CO decreased in the order of La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-R > La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-S > La 0.8Ce 0.2Ag 0.4Mn 0.6O 3-R > La 0.8Ce 0.2Ag 0.4Mn 0.6O 3-S. In NO-TPD experiments, the principal desorbed species detected in the effluent was NO with a trace amount of O 2 and N 2O, suggesting that the non-dissociated adsorption of NO on the surface of the perovskite-type oxides was dominant. The XPS results revealed that Ce 4+ and Cu + was the predominant oxidation state for Ce and Cu components in La 0.8Ce 0.2Cu 0.4Mn 0.6O 3 and La 0.8Ce 0.2Ag 0.4Mn 0.6O 3 catalysts. The existence of Cu + ions and its redox reaction (Cu + ↔ Cu 2+) would benefit the NO adsorption and reduction by CO. 相似文献
9.
The catalytic decomposition of acrylonitrile (AN) over Cu-ZSM-5 prepared with various Cu loadings was investigated. AN conversion, during which the nitrogen atoms in AN were mainly converted to N 2, increased as Cu loading increased. N 2 selectivities as high as 90–95% were attained. X-ray diffraction measurements (XRD) and temperature-programmed reduction by H 2 (H 2-TPR) showed the existence of bulk CuO in Cu-ZSM-5 with a Cu loading of 6.4 wt% and the existence of highly dispersed CuO in Cu-ZSM-5 with a Cu loading of 3.3 wt%. Electron spin resonance measurements revealed that Cu-ZSM-5 contains three forms of isolated Cu 2+ ions (square-planar, square-pyramidal, and distorted square-pyramidal). The H 2-TPR results suggested that in Cu-ZSM-5 with a Cu loading of 2.9 wt% and below, Cu + existed even after oxidizing pretreatment. The activity of AN decomposition over Cu/SiO 2 suggested that CuO could form N 2, but, independent of the CuO dispersion, nitrogen oxides (NO x) were formed above 350 °C. Cu + and the square-pyramidal and distorted square-pyramidal forms of Cu 2+ showed low activity for AN decomposition. Temperature-programmed desorption of NH 3 suggested that N 2 formation from NH 3 proceeded on Cu 2+, resulting in the formation of Cu +. The Cu + ions were oxidized to Cu 2+ at around 300 °C. Thus, high N 2 selectivity over Cu-ZSM-5 with a wide range of temperature was probably attained by the reaction over the square-planar Cu 2+, which can be reversibly reduced and oxidized. 相似文献
10.
Cu-ion-exchanged iron-pillared interlayer clays (Fe-PILCs) were prepared under different pH conditions to analyze the influence on the distribution of the copper species over their structure, and on the catalytic performance for the selective catalytic reduction (SCR) of NO x by propene. It was observed that for those samples prepared without pH control, the copper was as isolated Cu 2+ ions. When the samples were prepared under acid pH, the catalytic activity decreased and an appreciable CO production was observed, likely due to the low amount of Cu 2+ cations in those catalysts. Finally, for the samples prepared under alkaline pH, the copper was as Cu 2+ ions and CuO clusters. Their catalytic tests showed the best results for the SCR of NO x. The presence of CuO species led to an improvement in NO x yield to N 2. With the catalytic tests and a study by in situ FTIR of SCR of NO, a reaction mechanism has been proposed, where the reaction intermediates are mainly acetates, organic nitro compounds and nitrous oxide species. 相似文献
11.
Copper ion-exchanged zeolites ZSM5 with SiO 2:Al 2O 3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560–5400 h −1). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO 2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO2:Al2O3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm−1 is observed below the light-off temperature and interpreted as a bridged nitrato group bound to Cu2+–O–Cu2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrato groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N2O3, also binds in a bridge configuration to the same Cu2+–O–Cu2+ dimers. A second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm−1 probes isolated copper ions. A third infrared band at 2130 cm−1 confirms previous observations of
-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for
adsorption are blocked by Cu2+ ion-exchange. The 2130 cm−1 species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice. Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers. A high SiO2:Al2O3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites. 相似文献
12.
The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C 3H 6 over CuO/γ-Al 2O 3 has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu 0/Cu + to Cu 2+ by NO and O 2, (ii) the co-adsorption of NO/NO 2/O 2 to produce Cu 2+(NO 3−) 2, and (iii) the reaction of Cu 2+(NO 3−) 2 with C 3H 6 to produce N 2, CO 2, and H 2O. Increasing the O 2/NO ratio from 25.0 to 83.4 promotes the formation of NO 2 from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO 2/O 2. This reactant mixture allows the formation of Cu 2+(NO 3−) 2 and its reaction with the C 3H 6 to occur at a higher rate with a higher selectivity toward N 2 than the low O 2/NO flow. Both the high and low O 2/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C 3H 7---NO 2, C 3H 7---ONO, CH 3COO −, Cu 0---CN, and Cu +---NCO intermediates toward N 2, CO 2, and H 2O products. High O 2 concentration in the high O 2/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O 2/NO SCR at 523–698 K. High O 2 concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O 2 concentration at temperatures above 723 K. 相似文献
13.
NO TPD, H 2-TPR and XRD have been used to characterise copper-exchanged mordenites with different Si/Al ratios, copper contents and cocations. The results showed that copper is mainly in the form of isolated Cu 2+ ions in CuMOR catalysts with copper exchange ≤20%, whereas at higher copper exchange CuO species are also present. These results were obtained with H and Na as cocation and were achieved by changing either the catalyst Si/Al ratio or the copper content. The data also indicate that the cocation mainly affects copper location and that copper is more easily reduced in sodium form catalysts than in protonic form. It was found that the isolated Cu2+ ions are the most effective species for NO adsorption and the most active species for NO SCR. 相似文献
14.
The adsorption of N 2 on a copper ion-exchanged ZSM-5 sample (CuZSM-5) prepared by ion exchange using an aqueous solution of copper propionate, Cu(C 2H 5COO) 2, was examined at room temperature by measuring the FT-IR spectra, adsorption isotherms and heat of adsorption. This sample was found to be extremely efficient in terms of N 2 adsorption with regard to both the amount and the energy (i.e., heat) of adsorption, compared with samples prepared by a conventional ion-exchange method using an aqueous solution involving Cu 2+ and simple counter ions, Cl − or NO 3−. To clarify the specificity of the newly-prepared sample, the ion-exchange of ZSM-5 with Cu 2+ was carried out by employing aqueous solutions involving Cu 2+ and various types of counter ions [propionate (C 2H 5COO −), acetate (CH 3COO −), formate (HCOO −), chloride (Cl −) and nitrate (NO 3−) ions]. When the ion exchange was performed by using a Cu(C 2H 5COO) 2 or Cu(CH 3COO) 2 solution, the Cu 2+ species with propionate or acetate ligand (in the monomer state) were ion-exchanged in ZSM-5, as confirmed by the DR, EPR and FT-IR spectra for CuZSM-5. In contrast, Cu 2+ species were present in the form of aquo-complexes in samples prepared with other solutions. This distinct difference can be ascribed to the difference in the p Ka values of the counter ions; carboxylate ions, with a high p Ka value, are inclined to form a complex with Cu 2+. Using this newly applied Cu(C 2H 5COO) 2 solution, the present ion-exchange method has the potential to develop new effective materials that possess the specific adsorption and catalytic properties of CuZSM-5. 相似文献
15.
A combined Fourier transform IR (FT-IR) and electron paramagnetic resonance (EPR) study shows that copper in ‘excessively exchanged’ Cu/ZSM-5 is initially present as OH bridged Cu 2+ dimers, besides isolated Cu 2+ ions. Upon heating, the dimers lose water and become oxygen bridged [Cu---O---Cu] 2+ complexes. These are ‘EPR-silent’, presumably as a consequence of antiferromagnetic coupling of the unpaired electrons in each Cu 2+; they are, however, detectable by their perturbation of the lattice vibrations, detected by a FT-IR band at 918–923 cm −1. Reduction by hydrogen or carbon monoxide converts the [Cu---O---Cu] 2+ complexes to pairs of Cu + ions, while the color changes from green to grey. Reductive adsorption of nitrogen monoxide on Cu 2+ results in the formation of Cu +---NO +. Destructive thermal desorption of nitrogen monoxide at 100°C not only restores the Cu 2+ ions, but also appears to regenerate the [Cu---O---Cu] 2+ complex. The results suggest that pairs of copper ions are instrumental in the catalytic decomposition of nitrogen monoxide. 相似文献
16.
The selective catalytic reduction (SCR) of NO by hydrocarbon is an efficient way to remove NO emission from lean-burn gasoline and diesel exhaust. In this paper, a thermally and hydrothermally stable Al–Ce-pillared clay (Al–Ce-PILC) was synthesized and then modified by SO 42−, whose surface area and average pore diameter calcined at 773 K were 161 m 2/g and 12.15 nm, respectively. Copper-impregnated Al–Ce-pillared clay catalyst (Cu/SO 42−/Al–Ce-PILC) was applied for the SCR of NO by C 3H 6 in the presence of oxygen. The catalyst 2 wt% Cu/SO 42−/Al–Ce-PILC showed good performance over a broad range of temperature, its maximum conversion of NO was 56% at 623 K and remained as high as 22% at 973 K. Furthermore, the presence of 10% water slightly decreased its activity, and this effect was reversible following the removal of water from the feed. Py-IR results showed SO 42− modification greatly enhanced the number and strength of Brönsted acidity on the surface of Cu/SO 42−/Al–Ce-PILC, which played a vital role in the improvement of NO conversion. TPR and XPS results indicated that both Cu + and isolated Cu 2+ species existed on the optimal catalyst, mainly Cu +, as Cu content increased to 5 wt%, another species CuO aggregates which facilitated the combustion of C 3H 6 were formed. 相似文献
17.
A simple strategy of Cu modification was proposed to broaden the operation temperature window for NbCe catalyst. The best catalyst Cu 0.010/Nb 1Ce 3 presented over 90% NO conversion in a wide temperature range of 200-400 ℃ and exhibited an excellent H 2O or/and SO 2 resistance at 275 ℃. To understand the promotional mechanism of Cu modification, the correlation among the “activity-structure-property” were tried to establish systematically. Cu species highly dispersed on NbCe catalyst to serve as the active component. The strong interaction among Cu, Nb and Ce promoted the emergence of NbO 4 and induced more Brønsted acid sites. And Cu modification obviously enhanced the redox behavior of the NbCe catalyst. Besides, EPR probed the Cu species exited in the form of monomeric and dimeric Cu 2+, the isolated Cu 2+ acted as catalytic active sites to promote the reaction: Cu 2+-NO 3-+NO(g) → Cu 2+-NO 2-+NO 2(g). Then the generated NO 2 would accelerate the fast-SCR reaction process and thus facilitated the low-temperature deNO efficiency. Moreover, surface nitrates became unstable and easy to decompose after Cu modification, thus providing additional adsorption and activation sites for NH 3, and ensuring the improvement of catalytic activity at high temperature. Since the NH 3-SCR reaction followed by E-R reaction pathway efficaciously over Cu 0.010/Nb 1Ce 3 catalyst, the excellent H 2O and SO 2 resistance was as expected. 相似文献
18.
Nine different metal oxide catalysts were prepared by impregnating alumina washcoats with water solutions containing La 3+, Sr 2+, Cu 2+ and Ru 3+ ions and calcining them at 900°C. The produced samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) studies combined with energy-dispersive spectroscopy (EDS) analysis, X-ray powder diffraction and specific surface area measurements. A perovskite phase of the nominal composition La 1-xSr xAl 1-2yCu yRu yO 3 was found in all samples, in increasing amount in the samples with increasing contents of strontium and ruthenium. The catalysts were evaluated with respect to light-off temperatures and redox characteristics using two gas mixtures, one containing NO/CO/C 3H 6/O 2/N 2 and the other NO/CO/N 2. The light-off temperatures for nitric oxide reduction decreased from 534 to 333°C for the catalysts without and with strontium and ruthenium, respectively. In the presence of oxygen the conversion of nitric oxide declined rapidly under oxidative conditions whereas in absence of oxygen this decline was less pronounced and found to be linear over the entire redox interval studied. These studies suggest that the perovskite phase takes an active part in the conversion of nitric oxide and carbon monoxide to nitrogen and carbon dioxide. 相似文献
19.
Cu/Mg/Al mixed oxides (CuO = 4.0–12.5 wt%), obtained by calcination of hydrotalcite-type (HT) anionic clays, were investigated in the selective catalytic reduction (SCR) of NO by NH 3, either in the absence or presence of oxygen, and their behaviours were compared with that of a CuO-supported catalyst (CuO = 10.0 wt%), prepared by incipient wetness impregnation of a Mg/Al mixed oxide also obtained by calcination of an HT precursor. XRD analysis, UV-visible-NIR diffuse reflectance spectra and temperature-programmed reduction analyses showed the formation, in the mixed oxide catalysts obtained from HT precursors, mainly of octahedrally coordinated Cu 2+ ions, more strongly stabilized than Cu-containing species in the supported catalyst, although the latter showed a lower percentage of reduction. The presence of well dispersed Cu 2+ ions improved the catalytic performances, although similar behaviours were observed for all catalysts in the absence of oxygen. On the contrary, when the mixture with excess oxygen was fed, very interesting catalytic performances were obtained for the catalyst richest in copper (CuO = 12.5 wt%). This catalyst exhibited a behaviour comparable to that of a commercial V 2O 5–WO 3TiO 2 catalyst, without any deactivation phenomena after four consecutive cycles and following 8 h of time-on-stream at 653 K. Decreasing the copper content or increasing the calcination time and temperature led to considerably poorer performances and catalytic behaviours similar to that of the CuO-supported catalyst, due to the side-reaction of NH 3 combustion on the free Mg/Al mixed oxide surface. 相似文献
20.
ZSM-5 zeolites modified with Cu + ions were prepared either by the high-temperature chemical reaction of hydrogen form with CuCl vapour or by the wet ion exchange with subsequent reduction of the modified samples in CO at 873 K. Adsorption of H 2, N 2 or C 2H 6 by Cu + ions was studied by DRIFTS and by volumetric technique. The conclusions about the structure of adsorption complexes were supported by the DFT cluster quantum chemical calculations. The obtained results indicated that in addition to the previously reported strong adsorption of nitrogen, the univalent copper also unusually strongly adsorbs molecular hydrogen and ethane. Adsorption of hydrogen is the most amazing since the observed low-frequency shifts of the HH stretching vibrations were as high as about 1000 cm −1. This is quite different from much weaker H 2 perturbation by Cu 2+ cations. Adsorption of ethane by Cu + ions also resulted in the low-frequency shifts of some of CH IR stretching bands up to 400 cm −1. The DFT cluster modelling indicated that both adsorption of hydrogen and ethane could be explained by interaction with the isolated Cu + ions localized at the sites of the ZSM-5 framework. Quantum chemical calculations indicated the important role in the bonding of adsorbed hydrogen and ethane of electron back donation from d π-orbitals of Cu + ions to the σ *HH or CH orbitals. The overall yield of Cu + sites of the strong H 2 or N 2 adsorption is about twice lower than the total copper content. 相似文献
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